The invention relates to an electromagnetic buzzer having a vibration unit which is excited by an electromagnet transducer which induces a regularly varying magnetic field, and more particularly a buzzer with integrated electronic oscillation circuit which drives the electromagnet transducer.
A buzzer having a vibration unit which produces an audible signal in response to the excitation from an electromagnet transducer is known in several forms, which differ in the manner of exciting the vibration unit. In one practical form, a diaphragm formed of a magnetic material is magnetically excited in a direct manner. A modification thereof comprises a diaphragm of a non-magnetic material having an armature, formed by either permanent magnet or iron piece, mounted thereon, which armature is effective to cause an oscillation of the diaphragm. In another form, a diaphragm is physically impacted by a striker on a vibrating member which is in turn excited. In these forms of buzzers, an audible signal is produced as a result of the oscillation of the diaphragm. On the other hand, a further form of the buzzer is known. A striker on a vibrating member impacts the core of an electromagnet transducer, thereby producing a percussion sound. The present invention is applicable to either form of buzzer.
To induce a regularly varying magnetic field in the electromagnet transducer, the latter includes an electronic oscillation circuit such as a blocking oscillator. Such oscillation circuit is disclosed, for example, in U.S. Pat. No. 3,887,914 issued to Sato et al and No. 3,945,004 issued to Myers but the specific detail of such circuit does not form any part of the present invention.